The task was to create their own castle based on those they had studied. The Motte and Bailey castles (where the main building is on a small hill) was the first type of castle William the Conqueror built when he took control of Britain in 1066.
Inspired by the castles crusaders had seen in the Middle East, the stone keep with the living area protected by high curtain walls and made out of stone was a stronger, more durable improvement on the Motte and Bailey. As a result, many still exist today, the Tower of London being a famous example.
Here is just a small selection from the many wonderful castles that year 7 created: